1. Field of the Invention
The present invention relates in general to meters, and more particularly to meters of a transmitted illumination type which comprises a transparent board, a dial plate laid on the board, a transparent pointer moving over the dial plate and a light source for illuminating the dial plate from back and the pointer from within, by using the board as a light transmitting means.
2. Description of the Prior Art
In order to clarify the task of the present invention, one conventional meter of the above-mentioned type will be briefly described with reference to FIG. 10 of the accompanying drawings. The conventional meter is described in Japanese Patent Second Provisional Publication 53-2065.
In the drawing, denoted by numerals 1, 2, 3 and 4 are a housing, a movement, a translucent dial plate and a transparent pointer respectively. Denoted by numerals 5 and 6 are electric bulbs and denoted by numerals 7 and 8 are transparent light transmitting boards. Denoted by numeral 9 is a drive shaft extending from the movement 2 to the pointer 4. As is indicated by the arrow "P1", one part of light beams emitted from the electric bulbs 5 and 6 travels in the light transmitting boards 7 and 8 and reached to the pointer 4 to illuminate the same from within. Other part of the light beams from the bulbs 5 and 6 illuminates directly a back surface of the translucent dial plate 3 as is indicated by the arrow "P2" and illuminates the back surface of the dial plate 3 after being reflected by an inner wall of the housing 1 as is indicated by the arrow "P3". A ruled half-tone screen 35 is printed on a front surface of the dial plate 3. That is, in the dial plate 3, areas near the electric bulbs 5 and 6 are printed with condensed black dots to effect a greater light stopping and areas remote from the bulbs 5 and 6a are printed with scattered black dots to effect a smaller light stopping. With this ruled half-tone screen 3S, the dial plate 3 is evenly illuminated therethroughout.
However, printing the ruled half-tone screen onto the dial plate 3 needs a skilled, time-consuming and troublesome work and thus causes increase in cost of the meter. In fact, it is very difficult to apply even printing on various types of dial plates.